The present disclosure relates to a transfer unit which is incorporated in image forming apparatuses such as electro-photographic copiers, printers, facsimile machines, and multifunction peripherals having functions of these, and which transfers a toner image formed on an image carrier onto a recording medium such as a sheet which is electrostatically adsorbed onto a conveyance belt, and the present disclosure also relates to an image forming apparatus including such a transfer unit.
In image forming apparatuses, such as copiers, printers, and facsimile machines, using an electro-photographic method, a powdery developer (toner) is mainly used, and the following process is generally performed. That is, a photosensitive layer on a surface of a photosensitive drum (image carrier) is charged by a charging device to a predetermined surface potential (of the same polarity as charge polarity of toner), and then, an electrostatic latent image is formed on the photosensitive drum by an exposure device. Then, the resulting electrostatic latent image is visualized as a toner image with the toner in a developing device, the resulting toner image is transferred onto a sheet (recording medium) passing through a transfer section disposed facing the photosensitive drum, and thereafter, fixing processing is performed on the transferred toner image.
A known transfer unit is provided with a conveyance belt such that a toner image is transferred onto a sheet conveyed by being electrostatically adsorbed onto the conveyance belt. With this configuration, the conveyance belt is sometimes caused to meander or deviate from its position. The meandering or the deviation of the conveyance belt causes the position of a sheet under conveyance to shift in the sheet width direction, which is likely to invite inconveniences such as a displaced image transfer and a sheet jam.
To prevent such inconveniences, there has been proposed a method for automatically correcting meandering or deviation of the conveyance belt by detecting meandering or deviation of the conveyance belt by a sensor and adjusting the alignment (the angle in the belt thickness direction) of at least one suspension roller in accordance with the amount of meandering or the amount of deviation detected by the sensor. For example, there is known a belt conveyance device that includes meandering detection means which detects meandering of an endless belt, and an alignment adjusting mechanism which corrects meandering of the endless belt by adjusting the inclination of at least one suspension roller based on the detection result provided by the meandering detection means.
There is also known a belt conveyance device which has an endless belt and a plurality of rollers between which the endless belt is stretched, and which receives an image at a predetermined image receiving position on the endless belt, in the conveyance direction of the endless belt, directly or via a transfer member, wherein at least one of the plurality of rollers is a steering roller which is disposed on the upstream or downstream side of the image receiving position, and whose disposition angle with respect to the endless belt can be varied by inclining the steering roller.